The invention relates generally to the field of wind power generation, and in particular to wind farms having multiple wind turbine generators. Specifically, embodiments of the present technique provide a method and system to control power ramp down rate of a wind farm during high wind speed conditions.
Wind turbines are regarded as environmentally friendly and relatively inexpensive alternative sources of energy that utilize wind energy to produce electrical power. A wind turbine generator generally includes a wind rotor having a plurality of blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive a rotor of an electrical generator to produce electrical power. Modern wind power generation systems typically take the form of a wind farm having multiple such wind turbine generators that are operable to supply power to a transmission system providing power to a utility grid. Output from the wind turbine generators is typically combined for transmission to the grid.
Wind is an intermittent resource and power supplied by the wind farm to utilities is significantly influenced by changes in wind conditions. Generally, power output of a wind turbine power station increases with wind speed, until the wind speed reaches the rated wind speed for the turbine. With further increases in wind speed, the turbine operates at rated power up to a cut off value or a trip level. This is generally the wind speed at which dynamic loads on the wind turbine cause the mechanical components of the turbine to reach a fatigue limit. As a protective function, at wind speeds higher than a certain speed, wind turbines are often required to shut down, or reduce loads by regulating the pitch of the blades or braking the rotor, thereby leading to a reduced power output of the wind turbine generator, and consequently of the wind farm. However, electrical loads on utilities need to be balanced at all times by power generation units. Hence, utility systems usually have additional power generation resources available, such as thermal generators, that can accommodate this variability in wind conditions.
While the additional power resources can compensate for loss of power from wind farms, some amount of time is required to ramp up their output. For this reason, transmission system operators may require wind farms to control power ramp down rates during high wind speed conditions, particularly during high wind speed shutdown of the wind turbines. Such ramp down control is desirable in order to achieve compatibility between power ramp down rate of the wind farm and power ramp up rates of certain other generation resources supplying power to the utilities. This problem has not been coordinated at the wind farm level to control the aggregate shutdown and ramp down levels before wind turbines reach their high speed shutdown protective limits.
Accordingly, there exits a need for a technique to control operation of a wind farm so as to maintain power ramp down rate of the wind farm within desirable power ramp down rates during high wind speed conditions.